26th NARPM Training Program

Vapor Intrusion - Short Term Continuous Monitoring

A Case Study Bhooma SundarEPA Region 5

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Sub Slab Soil Gas

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Indoor Air TCE Discrete Data Points

CA-AIR-12 CA-AIR-17 CA-AIR-23

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Study Objectives

Employed high resolution continuous monitoring techniques to

- Gain a better understanding of the variability in the dataset;

- Recognize factors contributing to the variability;- Identify and assess preferential pathways; and- Determine the best path toward returning the

building to full industrial use.

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Observations Indoor air Source:

Atmospheric pressure and TCE concentration appear to be inversely proportional.

TCE concentrations increase as the pressure decreases. This correlation appears to be most apparent near the end of the sustained

drop in atmospheric pressure. In the restricted area, use of TCE containing products may have had more

impact on TCE concentration.

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ObservationsPreferential Pathway: The sump appears to be a potential vapor intrusion pathway

subsequent to significant rain events. Initially following a significant rain event, vapor intrusion is

suppressed due to pore space being filled with water. As the water continues to migrate downward, soil gas is displaced

to the surface and vapor intrusion temporarily increases

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ObservationsSub-slab Vapor Intrusion: Relatively low TCE concentrations were observed during periods of relatively high wind speed. These data suggest that a vacuum can be propagated through the subsurface; however, a sustained source of vacuum, such as an active fan, would be more effective at reducing sub‐slab pressures than relying on wind power alone.

In summary, data indicate that preferential pathway mitigation (2018) and the SSV improvements (2019) were successful in reducing TCE concentrations in the restricted building area.